The present invention relates to a flat gasket for a reciprocating engine or a driven machine including at least two laminated metal sheets 0.05-0.5 mm thick which are provided with a coating of an elastomer film at least on the side facing outward and have an edge area, formed by the outer contour and/or at least one cylinder bore and/or a water or oil passage in the cylinder head, adjacent to at least one peripheral first bead of one of the metal sheets, the second metal sheet bridging the first bead.
Flat gaskets for internal combustion engines or driven machines are known in a variety of embodiments, e.g., from German Patents 195 39 245, 195 31 232 and 42 05 824. In the case of engines for commercial vehicles, such cylinder head gaskets have the function of sealing the joint between the cylinder head and the cylinder block. They are usually made of one or more metal sheets joined together to form a laminate and have one or more combustion chamber passage orifices and one or more liquid passage orifices, the latter permitting coolant water and/or lubricant oil to pass between the cylinder head and the cylinder block. With conventional cylinder head gaskets, a complete bead in an edge area often encloses and seals the combustion chamber passage orifices. The liquid passage orifices are often also sealed by a bead surrounding the orifice in an edge area. On installation of the cylinder head gasket, the cylinder head and the engine block are pressed together by the bias force of the cylinder screws. The beads on the flat gasket lying between them are mutually supported against the adjacent sealing surfaces of the cylinder head or the engine block. The highest specific compressive load per unit area prevails in the immediate edge area of the combustion chamber passage orifices and in the area of the cylinder head screws. Stoppers surround the combustion chamber passages and act as deformation limiters. In addition to this static compressive load, the gasket is exposed to dynamic loads in operation of the engine. The distance between the sealing surfaces is not constant over time and space. Due to the periodic explosions in the combustion chamber, the cylinder head executes vertical and horizontal movements relative to the cylinder block. The amplitude of these sealing gap movements is greater, the greater the distance of the site in question from the cylinder head screws. A stationary condition over time cannot be achieved in the sealing gap either with the combustion chamber seal or the liquid seal. For a permanent and satisfactory seal, the gasket must be able to follow these relative movements for as long as possible through an elastically flexible response. The flat gasket must not lose its sealing elastic contact with the sealing surfaces of the cylinder block or the engine block. The functional lifetime of this elastic resiliency essentially limits the service life of the gasket. After a certain number of alternating load cycles, the spring characteristics of the flat gasket are reduced. At the end of the service life, leaking occurs in the seal of the combustion chambers or the chamber passage orifices.
The object of the present invention is to provide a flat gasket having an improved sealing effect, a high elastic resiliency, low manufacturing costs and a long operating life.
With the flat gasket according to the present invention, at least two laminated metal sheets are provided. One of these metal sheets has a bead which surrounds the orifice of a combustion chamber or a liquid passage. The other of these metal sheets bridges this bead, with the two metal sheets being permanently joined together on both sides of the bead. Due to this connection between the metal sheets, the flat gasket retains a very good elastic resiliency over a long period of operation. The sheet metal connection may completely enclose the orifice to be sealed or it may be designed in only spots or sections around the periphery, depending on the desired spring stiffness. The connection of the two metal sheets at the base of the bead causes the distance between the legs supporting the bead at the base of the bead to be essentially maintained when there is a reduction in the sealing gap. Thus, a reduction in the sealing gap causes a tensile stress on the metal sheet bridging the bead. The deformation of the bead is limited by the connection of the metal sheets. This increases the elastic resiliency. In sealing off the combustion gas or a liquid, the sealing effect is thus improved, because even with comparatively great sealing gap movements, the contact with the adjacent sealing surface of the cylinder head or the engine block is maintained. As a result of the construction according to the present invention, an additional enclosure for the combustion chamber may be omitted. The bead constructed according to the present invention assumes the function of the combustion chamber enclosure. A stopper which limits the compressive load in the edge area of the combustion chamber enclosure may thus be omitted. At the same time, a bead designed in this way guarantees that the sealing contact will be maintained around the combustion chamber even with relative movements of the cylinder head with respect to the cylinder block. What is true of the sealing system of the combustion chamber is also true of the liquid seal. Here again, the high elastic resiliency of the bead defined at the base has the result that the flat gasket is better able to follow the horizontal and vertical movements in the sealing gap over a longer operating time. The service life of the flat gasket is extended because the pressure forces against the sealing surfaces of the cylinder head and engine block are maintained for a longer period of time.
In cross section, the bead profile may have various shapes, e.g., a U shape or a triangular shape. The spring properties as well as the frictional behavior of the flat gasket with respect to the cylinder head or cylinder block may be adapted very satisfactorily to relative movements to be expected in the sealing gap through an appropriate design of the bead cross section.
The metal sheets may be made of the same or different materials, e.g., spring steel sheets. The metal sheets may also have different thicknesses. It is of course also conceivable for other materials to be used, such as metal gauze or plastic instead of the metal sheet.
The connection of the two metal sheets may be substantive, e.g., by welding, soldering or gluing. Depending on the stiffness, the weld may be along the periphery, either continuously or as an interrupted line or spot weld. The connection may also be produced inexpensively by electron beam welding.
The second metal sheet is preferably designed to be planar. A high stiffness of the elastic recoil may be achieved in this way.
It is advantageous if the second metal sheet has at least one second bead in an area of the first bead, the second bead being especially preferably designed to be different from the first bead. The cylinder head and engine block are usually made of different materials. Since each of the beads on the main surfaces of the flat gasket is designed differently, it is possible to design the flat gasket to be different in its spring properties with regard to its contact with the engine block or the cylinder head.
With regard to the manufacture of the flat gasket, it is advantageous to design the two beads to be in mirror image.
It especially advantageous if a third metal sheet is arranged between the first metal sheet and the second metal sheet and this third metal sheet is included in the connection between the first and second metal sheets. In particular when the third metal sheet has in the area of the first bead and the second bead a third bead having a differently shaped profile, the elastic behavior of the gasket with respect to the engine block or the cylinder head may be adapted very satisfactorily even with comparatively large sealing gap movements. By dividing the first or second bead as a partial bead, a larger contact area with the sealing surface of the engine block or the cylinder head is achieved. This makes it possible to prevent the bead of the flat gasket from digging into the surface of the engine block or the cylinder head.
It may be advantageous to bridge a comparatively large sealing gap through flat gaskets stacked one above the other.